Ⅰ. INTRODUCTION

Central odontogenic fibroma (COF) is an uncommon, slow-growing benign neoplasm of the jaw.¹⁾ COF occurs in a wide age group and has a female predilection.²⁾ It sometimes resembles an endodontic lesion when it occurs in the early days of its development. While the posterior region in the mandible is predominant with 55% prevalence, COF is usually involved in the anterior region when it occurs in the maxilla.³⁾ Clinical presentation shows an asymptomatic expansion of cortical bone, with the overlying soft tissue usually unaffected.^1),4) Radiologic presentation shows either unilocular or multilocular radiolucency with well-defined borders, and radiopacities are mixed with radiolucency. Dental root resorption and tooth displacement are common with lesion development. Differential diagnoses for a benign lesion of the jaws with similar clinical and radiographic features are fibrous dysplasia, calcifying odontogenic cyst, and central ossifying fibroma.

The purpose of this paper is to report a case of 45-yearold male patient and to analyze clinical and histological features of a central odontogenic fibroma.

Ⅱ. CASE REPORT

A 45-year-old Asian male visited the Department of Oral and Maxillofacial Surgery at Kyung Hee University Medical Center (Seoul, Republic of Korea) with gingival swelling in the right maxillary area. According to the patient, the lesion had developed slowly for 9 months with no other accom- panying symptoms of pain.

Oral examination of the patient revealed the presence of a dome-shaped mass from the right canine to the right molar region of the maxilla. The patient had lost several teeth because of periodontal disease with poor oral hygiene. The upper right second premolar was found to be displaced due to the expanded gingiva and mucosa of the lesion. (Figure 1) The mass was found to be firm without local heat and fluctuation on manual palpation. The overlying gingiva and mucosa were smooth and pink in color.

Panoramic radiography and cone-beam computed tomography (CBCT) images revealed intraosseous radiolucency with moderate-defined borders and diffusely scattered radiopacities ranging from the first premolar to the first molar (Figure 2A). Dental roots were intact; however, they were displaced. Expansion of the buccal bone was also observed (Figure 2B, 2C).

An incisional biopsy was performed for microscopic diagnosis before the operation. The lesion was surgically resected with a negative margin. The lesion was initially diagnosed as fibromyxoid lesion with ossification, consistent with odontogenic fibroma with involvement of resection margin.

The operation was carried out under general anesthesia. A sulcular incision and two vertical incision were made from upper right maxillary canine to upper right maxillary first molar in order to release the full thickness flap for better access to the lesion. The upper right maxillary sinus membrane was lifted meticulously by the lateral approach of the trap door window procedure by using an electric- motor drill with water cooling. The solid tumor was removed entirely with 4.3 × 5.5 × 1.6 cm in size (Figure 3). Buccal advancement flap technique was carried out for closing the operation site.

The cut surface of the mass revealed a grayish-white fibrotic mass with dispersed calcifications. Routine histopathological analysis using hematoxylin-eosin staining showed cellular fibroblastic tissue with bundles of collagen (Figure 4). Elongated fibroblastic cells with fusiform nuclei were found to be randomly distributed and densely packed in the myx-oid stroma (Figure 4A). Irregular calcifications or dentin-like materials were observed in the connective tissues (Figure 4B). Inactive odontogenic epithelium islands were detected in most areas of the lesion (Figure 4C). Giant cell reactions were detected because COF is sometimes associated with central giant cell granuloma (Figure 4D). Based on the clinical, radiographic, and histologic findings, a central odontogenic fibroma was finally diagnosed.

Post-operatively, wound healing was uneventful, and no complications, including sinus infection, sensory disturbance, and wound dehiscence, were noted. There was no incidence of recurrence during one year of follow-up.

Ⅲ. DISCUSSION

The patient presented a painless, slow persistent growth of intraoral appearance, and radiographic features corresponding to the characteristics of a benign tumor of the jaw. COF is an uncommon slow-growing benign neoplasm derived from mesenchymal tissue. It contains collagenous fibrous connective tissue with odontogenic epithelium.^3),5)

According to Gardner’s classification of odontogenic tumors, odontogenic fibroma is classified as “odontogenic ectomesenchyme with or without odontogenic epithelium” and COF can be divided into two different types based on the histological pattern.⁶⁾ The simple type of COF, the first type, includes fibrous tissue with collagen. The complex variant, or the World Health Organization (WHO) type, contains fibrous tissue with odontogenic epithelium in the myxoid area.^3),6) The complex type of COF sometimes includes cementum-like material and dysplastic dentin. Extraosseous or POF is associated with gingival tissue and tooth-bearing regions of the jaw, usually occurring along the anterior gingival region. POF is more common than COF and shows female predilection.

Clinically, COF resembles odontogenic and non-odontogenic tumors. It has a low persistent growth with painless cortical expansion. According to a systematic review by Pontes et al., several cases of COF were examined and reported to be predominant in the mandible and in females with a mean age of 30 years.⁷⁾ It is noticeable that our patient being a 45-year-old man with a calcified lesion located in the premolar in the maxilla has been diagnosed with COF.

Radiologically, COF often shows multilocular radiolucency; however, current reports have revealed unilocular radiolucency to be more frequent than multilocular radiolucency.^4),8) The former type of lesion is usually small, while the latter type is large and has a scalloped margin. Larger lesions include root resorption and displacement of the adjacent teeth. Our patient presented radiologic characteristics of both radiolucent and radiopaque flakes with an incidence of tooth displacement. It has been reported that less than 10% of COFs exhibit radiopaque flakes that correlate with calcification.^7),9) The presence of calcification in the present case led the surgeons to consider the lesion as a fibro-osseous lesion such as an ossifying fibroma.

Histopathologically, ossifying fibroma, which originates in the periodontal ligament, is composed of two main parts: stromal fibroblastic cells and bone deposits or cementumlike calcifications in the matrix.^10),11) Calcifications include numerous osteoid, woven bone, and lamellar bone exhibiting several different maturations. Similar to ossifying fibroma, the complex type of COF includes cellular fibrocollagenous tissue with calcifications and amyloid-like protein depositions. It is accompanied by scattered odontogenic epithelium as strands, cords, or nests in loose connective tissue. The presence of inactive odontogenic cells is the key to rule out histologic differential diagnosis.³⁾

Enucleation is considered the first choice of treatment for COF, and the lesion can easily be removed because of minimal bone adhesion and no tendency of it to transform into a malignant lesion.^12),13) These studies reported that the patients underwent surgical resection including the margin of the lesion due to the radiologically indistinct margin, and no margin involvement was confirmed by histological evaluation.

Although recurrence of COF is reported to be uncommon, the one in the maxilla may have a higher rate of recurrence than in the mandible.^7),14),15) Larger lesions of COF with multilocular lesions and displaced teeth tend to have a higher rate of recurrence because of the increase in shape and cortical destruction.^7),16),17) A review demonstrated only five cases of recurrence of COF in the literature; however, only 39 out of 68 cases were followed up; accordingly, the recurrence rate cannot be conclusive.¹⁵⁾

Ⅳ. CONCLUSION

The findings of this report show the importance of not only the clinical characteristics but also the radiographic and histologic examinations for diagnosis of the lesion. The clinical presentation alone was not sufficient to distinguish between similar disease entities. Therefore, it is necessary to thoroughly examine the lesion to rule out the differential diagnosis of a benign tumor of the jaw.